Solar Active Region and Quiet‐Sun Extreme‐Ultraviolet Spectra from SERTS‐95

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Abstract
Goddard Space Flight Center's Solar EUV Rocket Telescope and Spectrograph was flown on 1995 May 15 (SERTS-95), carrying a multilayer-coated toroidal diffraction grating that enhanced the instrumental sensitivity in its second-order wave band (171-225 Å). Spectra and spectroheliograms of NOAA active region 7870 (N09 W22) were obtained in this wave band with a spectral resolution (instrumental FWHM) ~30 mÅ and in the first-order wave band (235-335 Å) with a spectral resolution ~55 mÅ. Spectra and spectroheliograms of quiet-Sun areas northeast of the active region were also obtained. We derived the SERTS-95 relative radiometric calibration directly from flight data by means of density- and temperature-insensitive line intensity ratios. Most theoretical values for such ratios were obtained from the CHIANTI database. A total of 44 different lines were used to derive the relative radiometric calibration in the two spectral orders, most of them coming from seven (Fe X-Fe XVI) of the nine (Fe IX-Fe XVII) observed ionization stages of iron. The resulting relatively calibrated line intensities agree well with their corresponding normalized theoretical values. This supports the overall accuracy of the atomic physics parameters and demonstrates the power of the technique. The present work extends earlier work by Brosius, Davila, & Thomas, who determined the SERTS-95 second-order response using this technique. Many of the ratios employed here can be used to carry out a similar calibration exercise on spectra from the Coronal Diagnostic Spectrometer (CDS) aboard the Solar and Heliospheric Observatory (SOHO). We placed the line intensities onto an absolute scale by forcing our quiet-Sun He II λ303.8 + Si XI λ303.3 intensity to match that from previous observations. The resulting active region and quietSun absolutely calibrated line lists contain 127 and 20 lines, respectively. Active region densities derived from density-sensitive line intensity ratios of Fe X, XI, XIII, and XIV are mutually consistent with log ne ~ 9.4 ± 0.2; densities derived from Fe XII are significantly greater (log ne ~ 10).